National Motor Freight Classification (NMFC) is a freight classification system created by the National Motor Freight Traffic Association (NMFTA) and used for interstate, intrastate, and foreign commerce shipping of LTL cargo. NMFC freight codes provide standardized freight classes to determine the ease of transport of many of the huge variety of different commodities being shipped together in LTL shipments every year.
Freight classification groups products based on similar density, stowability, handling and liability so carriers and shippers have an effective way of communicating the ease of transporting said freight.
If you don't include an NMFC code on your BOL, it is very likely that your carrier will charge you a reclassification fee and charge you the cost of shipping the freight they determine your shipment is.